Journals Published by Vilnius Tech
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Robust optimization model of container liner routes in feeder line network
No full textThe universal application of the hub-and-spoke maritime network makes feeder line network key to restricting the quality and efficiency of maritime transportation. However, container liner routes in feeder line network are susceptible to the changes in shipment demand and international fuel prices. Therefore, based on the hub-and-spoke maritime network, this paper constructs a robust optimization model of container liner routes in feeder line network. Under the capacity and time constraints, routes optimization and ship equipment under uncertain environment are analysed. An improved tabu search algorithm was designed based on the characteristics of the model. The example analysis proves that the model can still ensure the robustness of routes under uncertain environment, which is more applicable than the deterministic model
Mathematical modelling electrically driven free shear flows in a duct under uniform magnetic field
Get PDFWe consider a mathematical model of two-dimensional electrically driven laminar free shear flows in a straight duct under action of an applied uniform homogeneous magnetic field. The mathematical approach is based on studies by J.C.R. Hunt and W.E. Williams [10], Yu. Kolesnikov and H. Kalis [22,23]. We solve the system of stationary partial differential equations (PDEs) with two unknown functions of velocity U and induced magnetic field H. The flows are generated as a result of the interaction of injected electric current in liquid and the applied field using one or two couples of linear electrodes located on duct walls: three cases are considered. In dependence on direction of current injection and uniform magnetic field, the flows between the end walls are realized. Distributions of velocities and induced magnetic fields, electric current density in dependence on the Hartmann number Ha are studied. The solution of this problem is obtained analytically and numerically, using the Fourier series method and Matlab
Solving a spectral problem for large-area photonic crystal surface-emitting lasers
Get PDFWe present algorithms for constructing and resolving spectral problems for novel photonic crystal surface-emitting lasers with large emission areas, given by first-order PDEs with two spatial dimensions. These algorithms include methods to overcome computer-arithmetic-related challenges when dealing with huge and small numbers. We show that the finite difference schemes constructed using relatively coarse numerical meshes enable accurate estimation of several major optical modes, which are essential in practical applications
A two-derivative time integrator for the Cahn-Hilliard equation
Get PDFThis paper presents a two-derivative energy-stable method for the Cahn-Hilliard equation. We use a fully implicit time discretization with the addition of two stabilization terms to maintain the energy stability. As far as we know, this is the first time an energy-stable multiderivative method has been developed for phase-field models. We present numerical results of the novel method to support our mathematical analysis. In addition, we perform numerical experiments of two multiderivative predictor-corrector methods of fourth and sixth-order accuracy, and we show numerically that all the methods are energy stable
A three-stage heuristic for optimizing container relocations in maritime container terminals
No full textThe Container Relocation Problem (CRP) is one of the most important optimization problems in maritime container terminals. The objective is to minimize the number of relocation operations for retrieving containers in a sequence. If the container to be retrieved next is not at the top of a stack, unproductive relocations have to be carried out. Due to the large number of containers handled by busy terminals, a slight reduction in relocation rates can result in significant savings in operating costs. Most of the existing heuristics make relocation decisions for the blocking containers one by one, based on simple indicators. In this article, we propose a Three-Stage Heuristic (3SH) that extends the decision horizon to multiple containers to achieve a higher-quality solution. Computational experiments are conducted on 3 sets of benchmark instances, and the results show that the proposed heuristic outperforms the state-of-the-art heuristics documented in the research literature
Railway transport system modelling approach for robustness analysis
No full textThe article presents an approach to train traffic modelling that allows for the analysis of how railway networks respond to various disturbances, including increased traffic and disturbance events. It discusses different methods of reconfiguration actions in key points of the railway network, which helps reduce delay propagation in the transport system. The 1st part covers building simulation models, which include defining infrastructure, setting train routes, configuring rolling stock, and disturbance scenarios, enabling the analysis of various disruptive events. The simulations allow for testing disturbance scenarios with minimal downtime risk without interfering with the real-world environment. The study results identified key system parameters generating the largest delays, such as platform availability, signaling, and the number of block sections. Probability density distributions for event intervals and durations were analyzed. The Kolmogorov–Smirnov test was used to confirm the fit of empirical distributions with theoretical ones, which were then implemented in the model of railway line No 271, running from Wrocław to Żmigród (Poland). As part of the reconfiguration of this railway line, new platforms were added, the time required for route setting was reduced, and the number of block sections was increased. These actions significantly reduced average delays, improved line capacity, and enhanced the robustness of the railway transport system against disturbances. The reconfiguration effectively reduced delays in areas causing significant time exceedances above 359 s, which was recognized in the Polish railway network as critical.
First published online 3 January 202
Investigation of aerodynamic characteristics of swept C-wing configurations at transonic speed using design of experiments and computational fluid dynamics
Get PDFAuthors investigated the aerodynamic characteristics of backward swept (BSCW) and forward swept (FSCW) C-wing configurations at transonic speed using Design of Experiments (DoE) and Computational Fluid Dynamics (CFD), aiming to enhance aircraft performance. Five geometric parameters for C-winglet design were identified from the literature. A quarter fractional factorial approach for the DoE was employed to analyse the effect of these parameters on aerodynamic characteristics at a constant Mach number and angle of attack of 0.8395 and 3.06°, respectively. Numerical results confirm the accuracy of the regression model in predicting aerodynamic coefficients, while normal plot highlight influential geometric parameters. Retrofitting C-winglets at the wingtips increases the aerodynamic performance by approximately 9.38% and 9.74% for BSCW and FSCW configurations respectively, compared to wings without C-winglets. The study demonstrates that utilizing a large cant angle and sweep angle of 60°, along with a low taper ratio of 0.562 for both the vertical and horizontal winglets, as well as a low cant angle of 90° for the horizontal winglet, reduces shockwave interactions on the C-winglet surface, consequently leading to a reduction in drag. It was concluded that the geometric parameters of the C-winglet play an integral role in designing new aircraft aimed at reducing drag
Enhancing UAS safety through building-induced dangerous zones prediction: concept and simulations
Get PDFThis study presents a comprehensive approach to operational estimation of the zones of danger for the Unmanned Aerial Systems (UASs) generated at low altitudes in presence of buildings, aimed at ensuring their safer operation. The main tasks are three. The first one is the definition of an inboard measurement methodology appropriate and feasible for UAS that allows Eddy Dissipation Rate (EDR) estimation. An inboard setup with a lightweight and low-cost anemometer operating at a 1 Hz sampling rate, immediately usable on UAS, is proposed. The second one is the definition of empirical equations to estimate the size of dangerous areas for the UAS flights around buildings through numerical simulation. The third one is the validation of the empirical formulas in a real-world case, through the numerical simulation of a group of buildings belonging to a research centre. Results show a good resemblance in the size of the danger zones, highlighting that this multi-faceted approach contributes to enhanced safety protocols for UASs operating in urban environments
Social production and consumption of space: study of public-market in Bandung, Indonesia
Get PDFThis paper aims to examine the role of architecture in social production and consumption of space, using public markets –architectural artifacts with rich social contents– as cases. This research adopts Low’s (2017) concept of social production of space and Dovey’s (2010) social constructivism of place to uncover the social production and consumption of public markets’ space. Cihapit and Pamoyanan market in Bandung, Indonesia, are selected as research cases, due to their cultural contents, appealing to consumers from middle to upper class society. It is found several roles of architecture in social production and consumption of public market space: building typology and morphology signifies historical context of development; architectural buildings contributes to formalize trading activities and elevating social class of market traders; commodities zoning is organized based on functional and socio-historical consideration; spatial intensity is determined by access and commodities zoning; informal atmosphere emerges as a distinctive advantage of public markets; and spatial quality is relative depends on governance capacity. Although normative criteria for good design can be formulated, in practice, spatial quality of public market is relative and depends on its capacity for spatial governmentality. By exploring social production and consumption of space and place provides broader perspective on the social practices of architecture, emphasizing its contribution for social and humanity studies
Enabling technologies challenges of green Internet of Things (IoT) towards sustainable development in the era of Industry 4.0
Get PDFThe extensive adoption of the Internet of Things (IoT) has increased the carbon footprint on a large scale across the globe. To handle this challenge, scholars and policymakers are making efforts to propose novel energy-efficient solutions to provide a desirable environment for green-IoT (G-IoT). Additionally, further research is required to analyze the G-IoT-related challenges to elucidate the difficulties of its implementation for researchers. Moreover, the GIoT requirements have been considered in different network levels, namely software, hardware, architecture, communication. To present a comprehensive framework to identify the challenges of G-IoT, a survey using literature review and expert’s opinion is carried. Total 23 challenges are taken to evaluate and implement G-IoT technologies towards sustainable development achievements (SDA). Consequently, this article aims to rank and evaluate the challenges to implement the G-IoT towards the SDA. An integrated approach is proposed with stepwise weight assessment ratio analysis (SWARA) and additive ratio assessment (ARAS) under Pythagorean fuzzy sets. As a result, an machine-to-machine (M2M) standardization protocol with a weight value of 0.0508 has the first rank, followed by adaptation to natural energy sources with a weight value of 0.0479, information security and privacy protection with a weight value of 0.0469, and internet protocol version-6 (IPv6) for low-end devices with weight 0.0467. To validate the proposed method, sensitivity analysis and comparison using existing methods have been conducted.
First published online 30 March 202